As opposed to a disposable primary battery, a secondary battery can be recharged repeatedly, and is being used not only in the field of high-tech compact electronic devices, such as, including mobile phones, personal digital assistants (PDAs), and laptop computers, but also as a source of power of energy storage systems and electric vehicles or hybrid vehicles.
For a device requiring high power such as a motor drive system in electric vehicles or hybrid vehicles or power storage systems, it is general to use a high capacity modularized battery in which a plurality of unit battery cells is stacked and connected in series or parallel.
On the other hand, a secondary battery generates a large quantity of heat during charge and discharge, and unless the heat is efficiently cooled, the service life of the secondary battery is shortened and a malfunction occurs, resulting in stability degradation, and in worse cases, leading to a fire and an explosion, so efficient cooling is an important task in the fabrication of a modularized battery including a secondary battery.
Also, for electric vehicles or hybrid vehicles, in the event that battery cells are subject to serious impacts or physical damage by a traffic accident, for example, a battery cell is damaged when pierced by a pointed object, an internal short occurs, leading to a fire or an explosion, and a driver or a passenger may be confronted by a dangerous situation.
On the other hand, a unit battery cell may be a can-type battery embedded in a prismatic or cylindrical case made of metal, or a pouch-type battery in which an electrode assembly and an electrolyte are embedded in a pouch packaging made of a sheet having a synthetic resin coating layer laminated on a main material, such as, for example, an aluminum foil.
A can-type battery has a higher physical strength than a pouch-type battery, while a pouch-type battery which is more lightweight and easier to fabricate is being widely used in recent days. However, a pouch-type battery has a disadvantage of poor resistance to expansion and an explosion resulting from an external impact or an internal short, that is, a low mechanical strength.
For these reasons, a modularized battery, in particular, a modularized battery using a pouch-type battery as a unit battery cell, employs a method which inserts and stacks a cartridge frame with a structure easy to receive and stack unit battery cells between the stacked unit battery cells as in Korean Patent No. 10-1307992 or Korean Patent No. 10-0921346.
FIG. 1 is a schematic perspective view showing an ordinary cartridge frame and a structure in which a plurality of unit battery cells is stacked using the same.
Referring to FIG. 1, an ordinary cartridge frame 2 has a structure which has an inter-cell separation plate 2a and a sidewall 2b so that a cell receiving part 3 which fits to a shape and a size of a unit battery cell 1 is formed.
The inter-cell separation plate 2a is generally made of metal having high thermal conductivity, such as, for example, aluminum, and absorbs heat generated from the battery cell 1 to cool the battery cell 1, and according to circumstances, the inter-cell separation plate 2a may have a refrigerant channel along the edges thereof, through which a cooling fluid flows, or a hole through which air passes.
On the other hand, the sidewall 2b is generally made of plastic, and it is not only because plastic is a material that is easy to manipulate by injection molding, but also because insulation should be ensured due to a risk of a contact between the sidewall 2b and an electrode terminal 1a of the battery cell in the manufacture and maintenance and repair of the battery module.
However, if the sidewall 2b of the cartridge frame 2 is formed of plastic, in the event of a fire or combustion of the battery cell 1, the sidewall 2b is prone to melt or combustion, causing a fire or combustion in other adjacent battery cell 1. This problem may be more serious in the case where a pouch-type battery is used as the unit battery cell 1. That is, in the pouch-type battery, a heat-sealing part 1b of a laminate sheet formed on the side surface of the battery cell 1 is structurally the most weak portion. Thus, when the battery cell 1 expands due to abnormal heat generation or internal gas in the battery cell 1, the side surface of the battery cell 1 is susceptible to burst. In this case, the sidewall 2b of the cartridge frame 2 made of a plastic material coming into contact with the side surface of the battery cell 1 is likely to melt or combustion by high temperature gas or flames emitting from the burst part.